A Glossary of Storage Terms and Acronyms

A Glossary of Storage Terms and Acronyms

Do you remember the old days when waiting for your computer to boot up meant you had enough time to visit the restroom, get something to eat, and maybe even mow your lawn? Now, with SSDs becoming more readily available, wake-up times for your computer are almost nonexistent. Go from a cold boot to browsing the Web in mere seconds with a M.2 NVMe SSD. But what does that mean? Read on to learn more about commonly used storage terms in this handy glossary.


Hard Disk Drive

The HDD is typically found in 2.5" or 3.5" form factors. They read and write data to spinning disks, or platters, which is measured in revolutions per minute (RPM).


Solid-State Drive

The SSD reads and writes data using flash memory. Unlike the HDD, the SSD has no moving parts so it’s less prone to mechanical failure. The SSD is also much faster than the HDD in terms of data transfer rates.


Solid-State Hybrid Drive

The SSHD combines a traditional HDD with a small SSD in one storage device. The SSD portion of the drive is used for quick access to commonly used data while the HDD portion is used for long-term storage. Apple has its own take on the SSHD, called the Fusion Drive.


Serial ATA

SATA is a physical connector that you use to connect an SSD or HDD to the motherboard.

SATA is also an interface standard. Most modern hard drives use SATA III, which can reach speeds of up to 6 Gb/s.


Serial Attached SCSI

SAS has a slightly different connector than SATA.

SAS is also an interface standard. Modern SAS-4 hard drives can reach speed of up to 22.5 Gb/s.

SAS drives also have higher mean time between failures (MTBF), but are usually only offered in lower storage capacities. SAS drives are typically used in enterprise environments, such as server farms.


PCI Express (Peripheral Component Interconnect Express)

PCIe is both a physical connector and a standard for high-speed components, such as SSDs and GPUs.

PCIe slots on a motherboard come in a variety of configurations, such as x1, x4, x8, and x16. The number after the x tells you the number of lanes the PCIe slot has.

PCIe standards come in different generations, where bandwidth is typically doubled for each newer generation. For example, PCIe 3.0 x16 has 32 GB/s of throughput while PCIe 4.0 x16 has 64 GB/s.


Non-Volatile Memory Express

NVMe is a host-controller technology that allows modern SSDs to optimize their read and write speeds. It essentially allows the SSD to operate through PCIe instead of SATA.

Please note that NVMe is not a physical connector, which is why NVMe SSDs are available in M.2, U.2, and PCIe variants.


NAND flash memory is a type of nonvolatile storage. It saves data as blocks, but has finite write cycles. There are different types of NAND flash storage, such as:

SLC – Single-Level Cell (1 bit per cell)

MLC – Multi-Level Cell (2 bits per cell)

TLC – Triple-Level Cell (3 bits per cell)

QLC – Quad-Level Cell (4 bits per cell)

SLC is the fastest, but has the highest cost. QLC is the slowest, but has the lowest cost.


M.2 is a physical connector used by SSDs. Its flexible physical layout allows for modules with different lengths to be used. M.2 can utilize the PCIe interface as well as SATA. M.2 replaced the mSATA standard.

Please note that M.2 is just the connector, which is why M.2 SSDs are available in NVMe, PCIe, and SATA variants.


U.2 is the connector used by select 2.5" SSDs (mostly Intel®). It utilizes the PCIe 3.0 x4 interface instead of SATA for faster read and write speeds.



A volume is a set amount of data storage that is formatted by a file system (i.e., NTFS), and typically has a drive letter assigned to it (such as C:, D:, E:, etc.) when viewed in an OS such as Windows. A volume is quite flexible. For example, a single hard drive can have multiple volumes. Alternatively, several storage devices can be linked together into a single volume.



A hot-swappable hard drive can be removed from a supported device without having to turn it off. These hard drives are typically used in RAID arrays and servers, where they need to be constantly running with no down time. When supported, you will be able to “hot-swap” a failed drive with a new drive to ensure storage is always available and your data is backed up accordingly.


Just a Bunch of Disk/Drives

Like the name suggests, JBODs are individual drives. This means that the Computer will see each drive as an independent disk volume. JBOD is easy to use, allowing you to add additional storage with ease. However, it does not provide any protection against hard drive failures, since there's no redundancy, like certain RAID modes.


Redundant Array of Independent Drives/Disks

As its name suggests, RAID is a way of combining multiple hard drives together into one system for data redundancy, improved performance, or even both. To learn more about different types of RAID arrays, please click here.


Network Attached Storage

NAS is a storage device that is connected to a network, which allows you to access it via the Internet from anywhere. To learn more about how to set up a NAS system, please click here.


The hard drive cache, also known as the disk buffer, acts as temporary memory for the hard drive as it reads and writes data. HDDs typically have 8 to 256MB of cache storage, while SSDs can have up to 4GB.


Input/Output Operations Per Second

IOPS is a common measurement used to benchmark a storage device. It determines the maximum number of read and write operations for a storage device.

While it is widely used, please note that IOPS does not guarantee real-world application performance.


Storage doesn’t always have to be local. With an Internet connection, you’ll have access to online cloud storage. You can make additional backups of your data and files to services, such as Google Drive, Microsoft OneDrive, Apple iCloud, and more.

Intel® Optane™ Memory

Intel® Optane™ Memory is a M.2 SSD that is designed to increase responsiveness in systems that have HDDs. It can improve boot times, file searches, large file transfers, and more. To learn more about Intel® Optane™ Memory, please click here.


NTFS – New Technology File System

This proprietary file system by Microsoft is natively supported by Windows. NTFS is the default file system for Windows and it is recommended if you’re working mostly with Windows systems. By default, Mac systems can only read NTFS and not write to them, although that could potentially change with the help of third-party drivers. NTFS does not have the same file size and partition limitations as FAT32.


FAT32 - File Allocation Table

FAT32 is a file system used primarily for older Windows systems. It is useful if you have older systems that do not support NTFS, but it does have some limitations. For example, individual files can only have a max file size of 4GB and a FAT32 partition is limited to 8TB. It is also missing other features present in NTFS, such as file permissions and other security features.


exFAT - Extensible Allocation Table

exFAT is a file system that can be natively read and written on Windows and macOS systems. Its versatility makes it the ideal format for USB flash drives and SD cards. It also does not have the same size limitations as FAT32.


APFS - Apple File System

Introduced with macOS High Sierra, APFS is the proprietary file system by Apple for its Mac systems. It is optimized for solid-state drives, although it will still work with mechanical and hybrid drives. APFS also provides other features, such as encryption, snapshots, and more.


HFS+ - Hierarchical File System Plus (AKA Mac OS Extended)

HFS+ is a proprietary file system by Apple and the predecessor to APFS. It is natively used in older Mac systems before macOS High Sierra, where it was then replaced by APFS as the default file system.

Thunderbolt™ 4

Developed by Intel® in a collaboration with Apple, Thunderbolt™ 4 is a hardware interface that utilizes the USB Type-C connector. Featuring a maximum throughput of 40 Gb/s when used with compatible devices, you’ll be able to transfer data quickly and efficiently with external HDDs and SSDs. Thunderbolt™ 4 can also support up to two 4K display simultaneously or a single 8K display.

USB 3.2

With updated USB naming standards, here’s a simple guide to USB 3.2:

USB 3.2 Gen 1 – 5 Gb/s

USB 3.2 Gen 2 – 10 Gb/s

USB 3.2 Gen 2x2 – 20 Gb/s

To learn more about USB, please click here.


USB4 is based on the Thunderbolt™ 3 protocol specification provided by Intel®. This means that USB4 can provide up to 40 Gb/s. USB4 improves bandwidth allocation, which means it can dynamically utilize multiple data and display protocols. USB4 also offers up to 100W of Power Delivery via USB Type-C.

Disclaimer: Support for Thunderbolt™ 3 is not mandatory for USB4. This means that not all computers with USB4 ports will work with Thunderbolt™ 3 or 4 accessories or peripherals.

Is there another storage term we didn’t cover that you would like to know about? Let us know in the Comments section, below.

1 Comment

You should also mention the various file systems like NTFS, FAT32, etc.